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Soap water treatment and reuse

I have made a reed bed for treating bath,wash basin and washing machine water. The aim was to reuse the water for gardening without doing major changes in the plumbing of existing houses. 

  • The reed bed  is planted with canna(kardaL in marathi) of the volume of approximately 3 times the input volume which gives 48 hours retention time. the reed bed is 2' deep, filled with gravel and sand. My output values are
  • cod: 50mg/l
  • bod3: 13.2mg/l
  • phosphate:8.53mg/l
I would like to know what values are expected for
  • watering the garden
  • car wash where the water will be sprayed
What are the critical parameters for using soap water? I have presently only considered phosphate.
Would the leaves of the garden plants turn yellow with excessive soap input?

The Central pollution control board of India specifies a BOD3 of 30mg/l , cod of  250mg/l and phosphates of 15mg/l  respectively for irrigation purposes. The laboratories in my city also generally only carry out the bod3 test. However the DEWATS book which I am using as a reference considers BOd5 values. 

  • I would like to know if the BOD 5 value will always be lesser than BOD3.My conjecture was that with more time of treatment the oxygen demand at the 5th day should be lesser than that on the 3rd day . Hence if my bod 3 value is satisfying the norms, my bod 5 value will automatically be much lesser and within the specified bracket. Please enlighten me on this.
  • Are the CPCB norms made assuming water for irrigation where there is always a base flow for running water and input of fresh water ? in my case there is no fresh water addition and the water is being directly used for the garden.
  •  Can someone give a guide on calculating retention time for kitchen water which is to be held in a grease trap, the values of which are

bod3: 72mg/l
cod: 180mg/l

  • The water would then be directly led into the reed bed and it should not be smelling.
  • This water which does not have any organic input,  is mainly soap water.  kitchen water has not been taken. Hence should the plants actually be given a soil base or should they be just on sand and gravel?

The above were two projects done in pune, a city where there is no scarcity, but high inequity of water. The water would thus be put to best use/reuse.

Many thanks in advance.


Pooja Joshi

095035 22444



1. Dear Pooja Joshi, 1. The

Dear Pooja Joshi,

  1. The ideal plants for 'reed bed' systems are ' reeds' which grow near the shores of lakes and ponds.In India, the reeds used successfully are called ' duck weed'. Reeds absorb atmospheric oxygen and release it through their roots.Since this treatment is essentially an aerobic process, reeds used must be capable of releasing atmospheric oxygen through their roots. If reeds are used, there is no problem of leaves turning yellow.
  2. The residence/retention time for best results is between 5 to 7 days for the water being treated in a reed bed system. This will bring the BOD level to 30 mg/lit (BOD5). For sizing, a reed bed tank must be 650mm deep and the Length to width Ratio must be from 1:1 to 1:3.
  3. Kitchen waste water can also be allowed into a reed bed. If the retention time is as per the figure I have mentioned above, oil and grease will also be taken care of. Make a reed bed system where there is ample sun light falling on it as this helps the reeds grow and improve the ' aeration' of the waste water.
  4. The output values for water emerging from her reed bed are OK. The water from the reed bed can be allowed into a tank which a layer of sand has supported on a bed of three to 4 layers of pebbles with largest at the bottom and smallest at the top on which sand is put. This will give treated water with suspended matter. Soil is not advisable.


Ion Exchange

2. Information on reed bed technology


We are a paragliding school located at Kamshet (near Pune) in the proximity of a lake.

We have a traditional septic tank + soak pit setup for use here at our base camp in the village. However, nowadays, we find the soak pits overflowing. We are keen to have a low cost  and eco friendly system for using/treating the water.

I wonder if you know someone who can help us set it up.

Peace, bliss & happy landings,

Sanjay & Astrid Rao

3. What is the daily flow of waste water?

Dear Mr. Rao,

The soak pits overflow when the percolation action is hampered due to excessive sludge and grease deposits. We have a microbial solution to these problems that not only help in restoring the soak pits but also enable you to recycle treated waste water for horticulture purposes.

It is a completely eco-friendly and an extremely cost effective solution. Your existing septic tank can be utilized and modified (if required) for the treatment.

We would require few details from your end to enable us to suggest the way forward-
1. Daily flow of waste water (from toilets, bathrooms, kitchen, laundry etc)
2. Dimensions of septic tank

Thank You.

Best regards,
Kush Agarwal
Ecologic Waste Solutions, +91-9899823242

4. How to divert grey water for flushing purpose, need help?

Dear Ranganathan,

I would like to implement use of greywater for toilet flushing in my new apartment in Bangalore. I would like to know if there are any agencies or individuals who can take up this project. Please advice.


5. response

Dear Pooja Joshi,
According to m  observation that you are carrying out basic filteration and not providing any nutrients and minerals, treating only grey waters with no admixes of black water ( main provider of nutrients and minerals) will always be difficult.

You need to introduce compost onto the soil of the plants so that they are healthy, and fine to carry out the cleaning process.

Send you some pictures of a wwt plant which is just being implemented, for plants to thrive and roots/ rhyzomes to provide bio- remediation it would take around 2 to 3 months.

This is a WWT plant on DEWATS principle design load 50 Kl per day.

It has septic tanks to start with and then filter- tanks with gravel / five stones media etc,

Then in the end have Root Zone Treatment- RZT

The sequences in pictures that you would observe are very clear, as below:

  • 0819- The plants being readied for planting
  • 0822- Planting in progress at Reed-Beds
  • 0828- ===== // ======
  • 0839- Planting and watering in progress
  • 0841- All plants in place

Download here

Pl furnishes me some data:

  1. What is the flow of ww per day?
  2. What is the size of your tank, and surface area of plantation.h how many plnts do you have?
  3. You require a minm. of 5 to 6 days retention,
  4. Plnts are getting nutrents from urine's N,P,K inference only
  5. The base plants when planted are done within a mud ball 8" dia- sphere with 1:4 (compost: soil) spaced 12" apart..These mud balls in the course of time gain a bio-regime of bio-sludges, humus and others decayed matter etc,,

Pl be in touch with data. And then we can plan out the best way of remedying the water.

Pl. keep up the good work of water- conservation.

Er. Ajit Seshadri,Head- Environment, The Vigyan Vijay Foundation

6. Dear Sir, Thanks a lot for

Dear Sir,

Thanks a lot for your input. Here is the data

  • The flow of waste water per day is 300ltrs
  • surface area of plantation is 2.5square meteres (26sqft)
  • depth is 0.6m
  • volume of water retained is 1500 ltrs ( effectively about 2-3 days retention considering volume of filter media inside)
  • I have presently planted the bed with 20 numbers of canna ( kardaL). We had planted some reeds ( Pankanis) earlier but the sand and gravel bed was harsh for their bulbs Presently I am also trying to see if australian phragmites (borTa) can take hold in the bed.  
  • About the point made earlier, Duckweed and pankanis grow just in water ( or very soft muck) where there is no actual base media. their roots only entangle and hold on to dead matter. So if I have to use reeds should I be totally avoiding a sand and gravel base and only keep a water holding tank with reads? Will that suffice in absorbing soapy waters. there is no fecal/kitchen input to the water.
  • According to me a planted gravel filter is done so that grey water never comes to the surface but instead flows under. This avoids mosquitos and other smells. The PMC also objects against open water bodies for fear of dengue. Ofcourse people maintain lotus beds but those are with fresh water addition and not grey water.
  • Plants are not getting any fecal or urine matter. It is only bath and washing machine water input. There is a natural addition of dead leaves and flowers which fall in the bed.
  • We made mudballs for the plant roots to take hold at the beginning.

Could you please send the link again as I am not able to open it.

Looking forward to your response. Thanks again.


Warm regards,


7. COrrected link

Hi Pooja,

The link works now we have corrected the error on the website -

Download here

8. After close to two years, here is an update

After close to two years from the first post here is an update:

1.The reed bed has excellent growth of Australian phragmitis and canna. The phragmitis took longer time to get itself established among the canna. However we trim the canna leaves every few months so that it allows the phragmitis to grow.

2.The dead leaves of canna and other leaves from neighbouring trees have deposited in the bed and created a good soil base. In these 2 years I have raked up the bed only once to ensure that no clogging is taking place.

3. Our garden to which the grey water is being fed is doing very well. There is no instance of leaf burning.

4. In the current dry season and heavy water cuts, it is a blessing to have this regular water source for our garden.

Pooja Joshi ,

9. Pooja, can you upload pictures of your work?

Dear Pooja,

Can you upload pictures of your work?


10. Some old pictures are uploaded in this link

The latest pictures are uploaded with india water portal and they shall hopefully add it on to this thread later.

You can also view the post on Grey water recycling: Reed bed for treating bath, wash basin and washing machine water in Pune here on IWP -


11. Reed bed turns black- have removed filter material - depth 8"

One experience of clogging happened in the reed bed where the output water started coming out to be jet black. I realized that an anaerobic process might be taking place. I concluded that water was being held back in the tank and not flowing out.

I removed half the filter material( mix of 40mm gravel+ fine sand )from the tank and have now retained only 8" depth of material . The material at the bottom has hardened like concrete. Over the past many months the plants have added biomass to the bed and due to overlying weight the bottom material has hardened and also turned black.

I have now loosened the remaining material and the blackness has reduced. With reference to Mr.SS Ranganathan's first reply, I shall now be planting more reeds and oxygen giving plants. More suggestions are welcome.

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